At 02:50 AM 4/12/2011, Phil Karn wrote:
To elaborate: ... As I recall, ARISSat-1 data frames can be up to 512 bytes long. Ignoring HDLC flags, bit stuffing, CRC, etc, that's 4K bits. At a data rate of 500 bps (the FEC is rate 1/2), 512 bytes will take 4096/500 = 8.192 seconds to transmit.
8.192 seconds is longer than 7.232 seconds.
Ooops.
But wait, there's more. If the satellite sends a series of back-to-back 512 byte frames, and the transmitter comes on too late after one has already started, you'll have to wait for it to end before you can begin decoding the next one. Meanwhile, the clock is quickly ticking down until the transmitter goes OFF again...
Double oops.
Hi Phil,
That's why it doesn't work that way.
In low power mode, the transmission is started clean every time. A single telemetry data frame is only 256 bytes so about 4 seconds of data. After the 1 frame, the transmitter is left on until the interleaver is emptied.
73, Tony AA2TX